The present invention relates to a method and apparatus for influencing the permeability of wrapping material for rod-shaped articles which constitute or form part of smokers' products. More particularly, the invention relates to a method and apparatus for influencing the permeability of wrapping material which is to be at least partially coated with an adhesive. Typical examples of materials which can be treated in accordance with the method of and in the apparatus of the present invention are continuous webs of cigarette paper, imitation cork and like wrapping materials which are subdivided into uniting bands for attachment of filter plugs or mouthpieces to plain cigarettes, cigars, cheroots or cigarillos. However, the method and apparatus of the present invention can be practiced with equal advantage in connection with the treatment of other types of porous wrapping materials which are used in the tobacco processing industry as wrappers of rod-like fillers consisting of natural, reconstituted or substitute tobacco and/or filter material for tobacco smoke. The rod-shaped articles which embody or are confined in portions of such wrapping material can constitute plain or filter cigarettes, cheroots, cigars or cigarillos and/or filter rod sections.
The popularity of gas-permeable wrapping material in the tobacco processing industry is on the increase since the discovery, or general acceptance of the belief, that the admixture of cool atmospheric air to tobacco smoke is likely to reduce the deleterious effects of tobacco smoke upon the health of a smoker. Atmospheric air can be admitted into tobacco smoke through pores or holes which are substantially uniformly distributed in the entire wrapping material and/or through holes or perforations which are machined into the wrapping material by resorting to one or more laser beams, sets of needles, spark generators and/or combinations of such and/or other perforating devices. In other words, the permeability of wrapping material is attributable to the porosity of such material alone, to the porosity and machine-made perforations, or solely to the presence of machine-made perforations. As a rule, perforations in the wrappers of filter cigarettes, cigars or cigarillos are formed in the wrappers of filter plugs close to the point where a filter plug abuts against the tobacco-containing part of the smokers' product. This suffices to ensure the inflow of requisite quantities of cool atmospheric air so as to exert a presumably beneficial influence upon the percentage of nicotine and condensates. The quantity of cool atmospheric air which is admixed to tobacco smoke should be maintained at a constant value, i.e., the permeability of each and every increment of the wrapping material (or at least of those portions of wrapping material which are intended to admit atmospheric air into the interior of the smokers' product) should be predictable and should match or very closely approximate a desirable optimum permeability. As a rule, the ratio of cool atmospheric air to tobacco smoke in the column of gaseous fluid that enters a smokers' mouth varies from brand to brand but should remain constant in a given brand of cigarettes, cigars or cigarillos. Even minor fluctuations in the permeability of wrappers of smokers' products of a given type are highly undesirable in view of the presumption that a certain minimum amount of cool air in the column of tobacco smoke is likely to greatly reduce the dangerous effects of smoke upon the health of a smoker.
Commonly owned German Offenlegungschrift No. 2,724,643 discloses a machine for the production of rod-shaped smokers' products wherein the wrappers of such products are tested for permeability and the apparatus for making holes or perforations is adjusted when the monitored permeability deviates from an optimum value. The testing is carried out by a pneumatic monitoring unit which establishes a pressure differential between the interior and exterior of the wrappers of successive articles and ascertains whether or not the pressure differential deviates from a range which is indicative of acceptable permeability. The higher pressure can be established in the interior of or around the wrapper, and the lower pressure can equal or be less than atmospheric pressure. Such procedure is acceptable when the manufacturer of cigarettes or the like is satisfied with a machine (e.g., a filter tipping machine) which is equipped with means for making perforations in a web of wrapping material and with means for adjusting the perforating means in dependency on the results of the testing operation.
On the other hand, many manufacturers of cigarettes or the like prefer to purchase wrapping material of certain permeability, i.e., a material whose permeability is or should be satisfactory to ensure the admission of a predetermined quantity of cool atmospheric air into the column of tobacco smoke. Thus, wrapping material of acceptable or presumably acceptable permeability is furnished by the manufacturer of such material. The manufacturer of wrapping material can furnish webs whose permeability matches or very closely approximates the desired permeability. Nevertheless, testing of smokers' products which include portions of such permeable wrapping material (in the form of wrappers of plain cigarettes, cheroots, cigars or cigarillos, in the form of wrappers of filter plugs or filter mouthpieces and/or in the form of uniting bands which cannot filter plugs or mouthpieces to plain cigarettes, cheroots, cigars or cigarillos) invariably or almost invariably reveals the presence of smokers' products wherein the permeability of wrappers deviates from an optimum permeability, i.e., the quantity of cool atmospheric air which is admitted to and mixes with the column of tobacco smoke does not match the desired optimum quantity. Such deviations of desirable permeability from actual permeability are especially frequent in filter tipped smokers' products, e.g., in filter cigarettes wherein plain cigarettes are connected with filter plugs or mouthpieces by means of foraminous adhesive-coated uniting bands. The permeability of such uniting bands is attributable to the porosity of wrapping material of which the uniting bands consist (such material normally includes cigarette paper webs or webs made of imitation cork) and/or to the presence of holes which are formed by mechanical and/or other means including lasers and spark generators.